In the food industry, plants (ovens, dryers, refrigerators, etc.) are known provided with endless conveyor belts on which the products to be treated are placed.
These known conveyor belts essentially comprise a plurality of metal bars, welded at their ends to the links of chains driven along guides extending along a predetermined path within the plant interior.
To enable the belt to be driven along a curved path, the individual bars must not be fixed together such that they preserve their parallelism, but instead must be able to also assume a slightly angled relative position, this being achieved by forming in each link, rigid with a bar, a longitudinal slot in which the adjacent bar engages.
These known conveyor belts are driven by two different methods: one of these consists of pulling the longitudinal belt spirally wound about a rotating drum, to the lateral surface of which the belt adheres with an edge by friction caused by the combined effect of the winding and the pulling; the other method consists of engaging an edge of the belt with a drive sprocket applied to its support structure.
In the first case the links welded to the ends of the individual bars are arranged for friction coupling to the surface of the rotating drum; in the second case the links welded to the ends of the individual bars are provided with outwardly projecting appendices which form overall a sort of articulated rack in which the drive sprocket can engage.
Examples of conveyor belts driven by the first method are described for example in EP1010648 and in US59541, while examples of conveyor belts driven by the second method are described for example in Italian utility model application MI2005U000149 and in Italian patent application MI2006A001395.
Italian utility model application MI2005U000149 of the same applicant already describes a conveyor belt of the aforesaid type, in which each chain link consists of a shaped plate having a flat appendix engageable by the sprocket teeth. This plate does not present an involute profile, and determines unsatisfactory engagement with the sprocket teeth, resulting in friction and wear. Moreover, the flat shape of the appendices poorly withstands the large stresses in play, with the passage of time they deforming because of the thrusts exerted by the teeth of the drive sprocket.
U.S. Pat. No. 7,762,388-B2 of the same applicant partly overcomes the limits of the preceding solution by forming the appendix of each chain link with complete involute profile. This solution has partly reduced the drawbacks related to the unsatisfactory coupling between the chain links and the drive sprocket, but has not completely solved the problem of the limited power transmissible by the drive sprocket to the chain links, as the open shape of the link appendices itself represents a limit to the maximum stresses which can be impressed on the appendices without causing deformation and loss of the involute profile.